1. Field of the Invention
The invention relates to a car reversal radar and, in particular, to a car reversal radar that automatically modifies its sensor scanning range and the method of the same.
2. Description of Related Art
In order for drivers to park the cars more safely and conveniently, cars are often installed with car reversal radars to avoid accidents caused by obstacles in the back. Common car reversal radars use ultrasonic sensors to send out ultrasonic waves and determine whether there is any obstacle by detecting the reflected waves. If the ultrasonic wave encounters an obstacle, it is reflected and received by the ultrasonic sensor. The actual distance between the obstacle and the sensor is then computed with the information of the speed of sound waves (340 m/s).
With reference to FIG. 4, the usual ultrasonic sensor 32 sends out fan-shaped ultrasonic waves, in stead of hemispherical. Therefore, there must be blind region 320 in the scanning region of the ultrasonic sensor 32. To minimize the blind region 320, the ultrasonic waves emitted by the ultrasonic sensor 32 should be as hemispherical as possible as shown in FIG. 5. However, the scanning region is too large in this case so that other obstacles that are not directly in the back of the vehicle may be detected. The driver is then misinformed to make possibly wrong decisions.
To solve the above-mentioned problem, some manufacturers design new ultrasonic sensors whose scanning region on the outer side is smaller than before. Such sensors are disposed on both edges in the back of the vehicles to prevent detection of obstacles on the sides of the cars. In this case, a vehicle has to be installed with two different types of sensors. Not only is this method difficult in installation and maintenance, it also increases the production cost.